It sounds like what you are looking for is an accomplished editor who can take your draft and polish it, along with some possible ghost writing to add as necessary. I am an experienced proofreader and editor, as well as a ghost writer. I can take your draft and polish it for story, content, continuity, character development, target audience, grammar, spelling, punctuation and English flow.
My most recent projects included editing a 4K-word non-fiction eBook in the history genre and an 85K word novel aimed at young adults who like history, science and adventure. Both authors were very pleased with my work.
Check out my portfolio. I am an accomplished writer and all the samples are my original work, which I edited and proofread myself.